Building a better battery

Mar 11, 2013

Scanning Electron Microscope image of micro-structures of cathodes made of carbon nanotubes and sulphur. Credit: Can Zhang

A new battery technology provides double the energy storage at lower cost than the batteries that are used in handheld electronics, electric vehicles, aerospace and defence.

The batteries used in these applications are typically based on lithium and a metal oxide, such as cobalt, manganese or nickel. Researchers from the University of Cambridge have developed a composite of sulphur and nanostructured carbon, for use as a battery cathode with much higher energy storage at much lower cost than conventional materials.

The cathode, or positive electrode, is one of three functional components of a battery, along with the anode (negative electrode) and electrolyte. The raw cathode materials are the single largest material cost in battery production, representing between 35 and 40 per cent of total costs.

The global lithium-ion battery market is expected to expand to $54 billion by 2020, up from $11.8 billion in 2010, driven primarily by demand from the consumer electronics and electric vehicle sectors.

"Using sulphur instead of the materials currently used in lithium-ion batteries could substantially reduce production costs, as sulphur is a fraction of the cost of other materials," says Dr Can Zhang of the Department of Engineering, one of the developers of the material. "Additionally, compared with conventional lithium-ion batteries, the carbon-sulphur electrodes achieve double the energy density per unit of weight."

The carbon-sulphur electrodes are produced by growing a "forest" of high-quality carbon nanotubes (CNTs) on a layer of metal foam. The CNT forest provides excellent electrical conductivity, and acts as a three-dimensional scaffold into which the sulphur is injected in order to form the cathode.

The sulphur is trapped within the scaffold in the form of small particles which store electrons. The pore structure of the metal foam, combined with the dense vertical packing of CNTs, provides a labyrinth with a large surface area for the retention of electrode material.

Despite their higher density and lower costs, the commercial development of lithium-sulphur batteries has been largely plagued by short cycle life, typically below 80 charge-discharge cycles. In comparison, a conventional lithium-ion battery will usually achieve 500 charge-discharge cycles. The CNT-sulphur composite significantly enhances the cycle performance of lithium-sulphur batteries, retaining 80% capacity after over 250 full charge-discharge cycles.

The work is the result of a collaboration between the groups of Professor John Robertson of the Department of Engineering and Dr Vasant Kumar of the Department of Materials Science and Metallurgy.

Dr Zhang, a postdoctoral researcher in Professor Robertson's group, has formed CamBattery to commercialise the technology, along with PhD students Bingan Chen, Kai Xi and Wentao He. The company won Technology Start-up of the Year at the 2012 Cambridge University Entrepreneurs competition.

Over the next two years, the team intends to build the first roll-to-roll machine to continuously produce the cathode material, and sell the product to major battery manufacturers. While the number of charge-discharge cycles achieved by lithium-sulphur batteries is not yet high enough for CamBattery to enter the consumer electronics market, applications in aerospace and defence are strong possibilities. "For aerospace and defence applications, energy storage takes precedence over life cycle," says Dr Zhang. "However, we will continue working at getting the number of life cycles high enough for consumer electronics and electric vehicles."

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User comments : 10

At only 500 discharge cycles electric cars that need to be charged every *day* (!) will last less than two years before the equivalent of a normal car's engine must be fully replaced. Our tax dollars at work!

At only 500 discharge cycles electric cars that need to be charged every *day* (!) will last less than two years before the equivalent of a normal car's engine must be fully replaced. Our tax dollars at work!

It will be interesting to find out what the end cost of these batteries will be once mass-produced, considering the abundance of the materials they use compared to lithium. At half the charge-discharge cycles but double the energy density it's still not a toss-up, because the low range of electric vehicles has been a complaint by many, but if the battery is then half the cost of lithium-ion batteries then the fact that they need to be changed more frequently could be overlooked, especially if replacement is made simple.

This always the same story: "Continue the way you are doing,( Spilling Energy, and pay for it), we have a way and the technologyto continue!!!"First it was Hydrogen, then cold fusion, then electrich cars with superb ............. Pellets, Solar, and so on.

It seems reports of amazing new battery tech, that's about 3 to 5 years away, comes out every other year with no actual production.

There is more to having new products than inventing stuff.New products require new investments (in new manufacturing facilities, resource procurement, etc.) If a manufacturer will not make more money off of a product based on new tech than on the one he's currently manufacturing then you won't see anyone turning this stuff into products.

After all: if a manufacturer makes a new car battery that has 10 times the charge he will only sell 1/10th he's currently selling. (Not a perfect example, since demand would surely increase, but you get the point)That's one problem of capitalism: You don't get the best product - just the one that makes most profit.

But ultimately this site is about science. If you have a gripe about people not making products based on new findings you're on the wrong site.

This is also an incremental improvement, which is much more conducive to a product becoming reality than a 'breakthrough discovery'. Production cost of these should be less than lithium-ion, which means a potentially larger profit-margin for the manufacturer while still likely being cheaper for the consumer. It also answers the longer range desire that most consumers have when it comes to electric cars. When it's a bunch of minor improvements the likelihood that the product will see the light of day is significantly better than a world-changing concept that turns out to be someone's bad math. Look at computers. There have been many reports of breakthroughs that will make computers hundreds of times faster, but the incremental improvements HAVE made them hundreds of times faster than what they used to be.

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